1. Technical Field of the Invention
The present invention relates to servo field detectors, disk drives and related methods.
2. Description of Related Art
As is known, many varieties of disk drives, such as magnetic disk drives are used to provide data storage for a host device, either directly, or through a network such as a storage area network (SAN) or network attached storage (NAS). Typical host devices include stand alone computer systems such as a desktop or laptop computer, enterprise storage devices such as servers, storage arrays such as a redundant array of independent disks (RAID) arrays, storage routers, storage switches and storage directors, and other consumer devices such as video game systems and digital video recorders. These devices provide high storage capacity in a cost effective manner.
As a magnetic hard drive is manufactured the disk is prerecorded at the factory, servo data is recorded on the disk in a plurality of servo wedges that are contained in radial segments about the disk. For each track on the disk, each servo wedge contains a servo field that is recorded with a preamble, a synchronization mark and servo data. Examples of servo data include a servo address mark, wedge number, track number, and burst data used by a disk controller to control the rotation of the disk and the position of the read/write heads of the disk drive. The preamble is traditionally coded with a 2T pattern of alternating 1's and 0's that is recorded on the magnetic medium of the disk. The read channel of the disk drive detects the beginning of a servo wedge by detecting the presence of the preamble.
Traditionally, the preamble of the servo field is detected using a sinusoidal matched filter that corresponds to the read signal generated by the read heads in response to the preamble pattern when the disk is at steady state. However, a frequency offset in the read signal, such as during a cold start of the drive, can easily cause a preamble to be missed. Missing the preamble causes the disk controller to miss the entire servo field, denying the disk controller information it uses to generate accurate timing and control information. Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of ordinary skill in the art through comparison of such systems with the present invention.